RenderBlockFlows with no children should not even try to run inline l…

…ayout

https://bugs.webkit.org/show_bug.cgi?id=254391

Reviewed by Antti Koivisto.

1. RenderBlockFlow's initial state is m_childrenInline = true
2. m_childrenInline is set to true when the block ends up with no children.
3. childrenInline() makes RenderBlockFlow run inline layout.

Initiating layout (IFC or BFC) does not make much sense when there's nothing to run layout on.

* Source/WebCore/rendering/RenderBlockFlow.cpp:
(WebCore::RenderBlockFlow::layoutInlineChildren): RenderSVGText calls layoutInlineChildren with no children :|

Canonical link: https://commits.webkit.org/262077@main

Source/WebCore/rendering/RenderBlockFlow.cpp

@@ -741,6 +741,18 @@ void LeadingTrimmer::adjustLeadingTrimAfterLayout()
 
 void RenderBlockFlow::layoutInFlowChildren(bool relayoutChildren, LayoutUnit& repaintLogicalTop, LayoutUnit& repaintLogicalBottom, LayoutUnit& maxFloatLogicalBottom)
 {
+    if (!firstChild()) {
+        auto logicalHeight = borderAndPaddingBefore() + borderAndPaddingAfter() + scrollbarLogicalHeight();
+        if (hasLineIfEmpty())
+            logicalHeight += lineHeight(true, isHorizontalWritingMode() ? HorizontalLine : VerticalLine, PositionOfInteriorLineBoxes);
+        setLogicalHeight(logicalHeight);
+
+        repaintLogicalTop = { };
+        repaintLogicalBottom = { };
+        maxFloatLogicalBottom = { };
+        return;
+    }
+
     if (childrenInline()) {
         auto leadingTrimmer = LeadingTrimmer { *this, this };
         layoutInlineChildren(relayoutChildren, repaintLogicalTop, repaintLogicalBottom);
@@ -773,6 +785,8 @@ void RenderBlockFlow::layoutInFlowChildren(bool relayoutChildren, LayoutUnit& re
 
 void RenderBlockFlow::layoutBlockChildren(bool relayoutChildren, LayoutUnit& maxFloatLogicalBottom)
 {
+    ASSERT(firstChild());
+
     LayoutUnit beforeEdge = borderAndPaddingBefore();
     LayoutUnit afterEdge = borderAndPaddingAfter() + scrollbarLogicalHeight();